Use axios instead of vue resource - step 1

What does this MR do?

Step 1 of using axios instead of vue resource:

1. Updates the docs on how to use
2. Updates the docs on how to mock tests
3. Adds axios-mock-adapter to make tests easier
4. Adds axios utils to enable crsf token in all requests & wait_for_requests
5. Uses new code in clusters an job view

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

#39727 (moved)